Ultrasonic imaging and treatment probe having an asymmetric focal zone

ABSTRACT

The invention relates to a treatment probe for focused ultrasound including a probe body, which is mounted in rotation around an axis; an elongated treatment transducer with a focused ultrasound emission acoustic axis, which is more or less the same as the rotation axis of the probe body; and an imaging transducer, the imaging plane of which contains the acoustic axis of the treatment transducer. The inventive probe can be used to provide a simple treatment. The probe body can be rotated around the axis in order to vary the direction of the imaging plane without moving the focus, which always remains in the imaging plane. The treatment transducer can be extended in order to provide safer treatment in relation to the organs to be treated and without risk of damaging the fragile surrounding organs.

FIELD OF THE INVENTION

The present invention relates to the field of focused ultrasound, andmore precisely, to treatment by focused ultrasound.

BACKGROUND OF THE INVENTION

Focused ultrasound makes it possible to treat deep tissues withoutdirect access to these tissues. A focused ultrasound beam originatingfrom a power transducer is concentrated towards a focus which ispositioned on the target. This results in a double thermal andcavitation phenomenon. The tissue effect depends on the application ofthe ultrasound energy. Under certain conditions (moderate acousticintensity), a thermal effect is obtained, under others (strong acousticintensity), the cavitation effect predominates. The choice of treatmentparameters (acoustic intensity and frequency, duration of firing,duration of pauses between the firings, spacing between the firingsetc.) is made in order to avoid burning in the intermediate tissues,i.e., situated between the ultrasound source and the target. Thedesignation “acoustic axis” of the transducer is given to a line joiningthe center of the transducer, or its center of symmetry (if it exists)and the focus. In the case of a plane transducer and electronicfocusing, the acoustic axis is the axis perpendicular to the transducerplane, and passing through the focus; the acoustic axis can alsogenerally be defined as passing through the focus and directed followingthe mean direction of ultrasound propagation.

The effect of each ultrasound pulse is generally limited to a smallspatial zone, in which the intensity of the ultrasound field isstrongest, and which is situated around the focus. The focal zone willtypically have the shape of a cylinder 1.5 mm in diameter in a planeperpendicular to the acoustic propagation direction and 10 mm in lengthin the acoustic propagation direction.

This technique is particularly useful when the treatment must beprecise, for example when the zone to be treated is close to sensitiveorgans to be preserved. This is the case for example with treatment ofthe prostate, in which the external sphincter must not be touched forfear of causing incontinence in the patient.

It has therefore been proposed to combine in one therapy appliance atreatment transducer and an imaging transducer; in fact ultrasoundmarking is useful because it is simple, inexpensive and emits noionizing radiation. The imaging transducer is used, as its nameindicates, to obtain an image of the zone to be treated. The treatmenttransducer, or power transducer, is used for the emission of theultrasound intended for the treatment. From the quantitative point ofview, the average power range for the imaging transducer is typically ofthe order of 0.1 to 1 W, while the average power range for the treatmenttransducer is typically of the order of 5 to 100 W. Moreover, theultrasound pulses emitted for the imaging have a typical duration of 0.1μs to 1 μs, whilst the therapy pulses last from 0.1 s to 20 s. In orderto make it possible to visualize a volume containing the target, adisplacement of the imaging transducer scanning plane can be provided.

Ultrasound therapy appliances combined with ultrasound scanning havebeen described. In EP-A-0 148 653, EP-A-0 162 735 and U.S. Pat. No.5,431,621, an imaging transducer is accommodated in the center of a capserving as treatment transducer; this cap has axial symmetry. Thescanning plane of the imaging transducer contains the acoustic axis ofthe treatment transducer. The ultrasound imaging transducer can turn onits axis, but this is not the case with the treatment transducer. It isproposed in these documents to use the appliance to destroy renalcalculi by shock waves or to treat tumors by hyperthermia.

WO-A-92 15253 describes a bevelled endorectal probe. The probe ismounted in rotation on a support and in translation along itslongitudinal axis. The treatment transducer is fixed with respect to theprobe body. The probe has an imaging transducer, which is fixed ormobile with respect to the treatment transducer. In all cases, theimaging transducer's scanning plane contains the focus of the treatmenttransducer.

EP-A-0-714 266 describes an endorectal probe suitable for treatment ofthe prostate. The probe comprises retractable therapy and imagingtransducers. In the “imaging” position, the second transducer scans aplane containing the acoustic axis of treatment. The scanning plane isvariable, as it can pivot about this axis. The treatment transducer doesnot turn about its acoustic axis, but about an axis which is parallel tothe axis of the endorectal probe.

WO-A-89 07909 discloses, in FIG. 2, an extracorporeal treatmentappliance comprising an imaging transducer and a treatment transducer.Each of the transducers is mounted at the end of a tube; the two tubesare mounted on a disk and extend perpendicularly to the plane of thedisk. The disk is mounted in rotation in the appliance. The tubecarrying the treatment transducer is approximately in the center of thedisk; this tube is mobile in translation along its axis. At the end ofthe tube, the treatment transducer is mounted in rotation on an axisperpendicular to the axis of the tube. The treatment transducer thus hasthree degrees of freedom, in order to be oriented in all directions. Theimaging transducer is mounted in analogous fashion; in all cases, thescanning plane of the imaging transducer contains the focus of thetreatment transducer. The axis of rotation of the disk—which is thelongitudinal axis of the tube carrying the treatmenttransducer—generally corresponds neither to the acoustic axis of thetreatment transducer, nor to that of the imaging transducer; in fact,for a given treatment depth, the scanning movement of the target throughthe focal point is carried out by rotation of the treatment transducerabout the axis perpendicular to the tube.

WO-A-95 02994 discloses, in FIG. 5, a probe suitable for visualizing andtreating tissues situated in the probe's longitudinal axis, such asliver tumors or fibromas. This probe has an imaging transducer and atherapy transducer mounted back to back, the whole assembly beingmounted in rotation at the end of the probe, about an axis perpendicularto the axis of the probe. The rotation of the probe body makes itpossible to modify the scanning plane of the probe. The rotation of thetransducers ensures scanning or treatment in the plane concerned. As inthe preceding document, the axis of rotation of the probe body—which isthe longitudinal axis of the probe—does not generally correspond to theacoustic axis of the treatment transducer. EP-A-0 273 180 discloses aprobe of the same type.

These different appliances of the state of the art are only slightly ornot at all suitable for the treatment of organs from outside the body,and for example for focused ultrasound treatment of the thyroid. A needtherefore exists for an appliance which can treat organs such as thethyroid, by focused ultrasound, simply, with precision, and effectively.

SUMMARY OF THE INVENTION

In one embodiment, the invention provides a focused ultrasound treatmentprobe, which is suitable for treatment of different organs from outsidethe body. The probe has a probe body which is mounted in rotation on asupport. The probe body comprises an elongated treatment transducer, theacoustic axis of which is substantially the same as the axis of rotationof the probe body. The probe body also has an imaging transducer, thescanning plane of which contains the acoustic axis of the treatmenttransducer.

The fact that the transducer is elongated allows high-precisionemission: the cone formed by the acoustic waves is asymmetrical and hasan angle at the apex—at the focus—which is less open in the transversedirection of the transducer than in the longitudinal direction of thetransducer. It is easier to avoid the organs close to the target. Thefact that the acoustic axis is substantially the same as the axis ofrotation of the probe body ensures that the probe body can turn aboutthe axis of rotation, without however the position of the focus withrespect to the target moving. It is then possible to displace the probebody in rotation, for imaging or treatment, without however displacingthe transducers.

As the scanning plane—or imaging plane—of the imaging transducercontains the acoustic axis and therefore also contains the axis ofrotation of the probe body, the target being situated at the focus ofthe treatment transducer remains in the imaging plane during rotation ofthe probe body.

The invention moreover proposes that the treatment transducer be mountedso that it is mobile in the probe body. It is in particular possible forthe treatment transducer to be mounted in rotation in the probe bodyabout an axis perpendicular to the axis of rotation.

This configuration makes it possible for the imaging transducer to alsobe mounted so that it is mobile in the probe body. It can in particularbe mounted in translation in the probe body, preferably following adirection parallel to the axis of rotation.

In one embodiment, the treatment transducer has an aspect ratio greaterthan 1.2. It is also advantageous for the treatment transducer to havean aspect ratio smaller than 2.5.

Preferably, the imaging transducer is an array carrying out a linearscan. It is then advantageous for the axis of this transducer to beparallel to the longitudinal direction of the treatment transducer. Theimaging transducer can in particular be integrated into the treatmenttransducer.

In another embodiment, the probe has a support on which the probe ismounted in rotation, the support displacing the probe in translation ina plane perpendicular to the axis of rotation. In this case, the supportcan moreover displace the probe in translation following the directionof the axis of rotation.

The support can also have a ball-and-socket joint for orientation of theprobe. Another solution is for the support to have an arch along whichthe probe moves; it is then advantageous for the radius of the arch tobe substantially equal to the distance between the arch and the focus ofthe treatment transducer.

A subject of the invention is therefore a focused ultrasound treatmentprobe, comprising a probe body mounted in rotation about an axis, anelongated treatment transducer, with an acoustic axis of focusedultrasound emission substantially the same as the axis of rotation ofthe probe body, an imaging transducer the imaging plane of whichcontains the acoustic axis of the treatment transducer.

According to one embodiment, the treatment transducer is mounted so thatit is mobile in the probe body.

According to another embodiment, the treatment transducer is mounted inrotation in the probe body preferably about an axis perpendicular to theaxis of rotation.

According to yet another embodiment, the imaging transducer is mountedso that it is mobile in the probe body.

According to yet another embodiment, the imaging transducer is mountedin translation in the probe body, preferably following a directionparallel to the axis of rotation.

It can also be provided that the treatment transducer has an aspectratio greater than 2.2. It can advantageously be provided that thetreatment transducer has an aspect ratio smaller than 2.5.

According to one embodiment, the imaging transducer is an array carryingout a linear scan.

According to another embodiment, the imaging transducer axis is parallelto the longitudinal direction of the treatment transducer.

According to yet another embodiment, the imaging transducer isintegrated in the treatment transducer.

According to yet another embodiment, the probe has a support on whichthe probe is mounted in rotation, the support displacing the probe intranslation in a plane perpendicular to the axis of rotation.

It can moreover be provided that the support moreover displaces theprobe in translation following the direction of the axis of rotation.

According to one embodiment, the support has a ball-and-socket joint fororientation of the probe.

According to yet another embodiment, the support has an arch along whichthe probe moves.

According to another embodiment, the radius of the arch is substantiallyequal to the distance between the arch and the focus of the treatmenttransducer.

Other characteristics and advantages of the invention will becomeapparent on reading the following description of embodiments of theinvention, given by way of example and with reference to the attacheddrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagrammatic view in longitudinal section of a probe,following the longitudinal direction of the treatment transducer;

FIG. 2 is a diagrammatic view in longitudinal section of the probe ofFIG. 1, following the transverse direction of the treatment transducer;

FIG. 3 is a diagrammatic view of the face of the probe of FIGS. 1 and 2;

FIG. 4 is a diagrammatic view of the probe of FIGS. 1 and 2, being usedfor treatment of the thyroid;

FIGS. 5, 6 and 7 are diagrammatic views corresponding to FIGS. 1, 2 and3, when the probe is in the imaging position;

FIG. 8 is a partial diagrammatic view of another example of a probe, inlongitudinal section following the longitudinal direction of thetreatment transducer;

FIG. 9 is a partial diagrammatic view of the face of a probe of FIG. 8;

FIGS. 10 and 11 are views of the position of the probe body with respectto a patient, being used for treatment of the thyroid;

FIG. 12 is a diagrammatic view of an example of a probe, showing theprobe support;

FIG. 13 is a view analogous to that of FIG. 12, for another example of aprobe support;

FIG. 14 is a flowchart showing treatment using a probe; and

FIG. 15 is a view of the treatment transducer explaining the firingparameters.

DETAILED DESCRIPTION

In this written description, the use of the disjunctive is intended toinclude the conjunctive. The use of definite or indefinite articles isnot intended to indicate cardinality. In particular, a reference to“the” object or thing or “an” object or “a” thing is intended to alsodescribe a plurality of such objects or things.

FIGS. 1 to 7 show an example in which the treatment transducer and theimaging transducer are mobile in the probe body; in contrast, FIGS. 8and 9 show an example in which the treatment transducer and the imagingtransducer are fixed in the probe body.

FIG. 1 is a diagrammatic view in longitudinal section of a probe,following the longitudinal direction of the treatment transducer. Thelongitudinal section of the probe is made in a plane containing the axisof rotation of the probe body; it can be seen in the example in FIG. 1that the probe body is elongated in shape and that the longitudinal axisof the probe body is the same as that of the axis of rotation. Thelongitudinal direction of the transducer is defined, due to theelongated shape of the treatment transducer, as the direction followingwhich the treatment transducer has the largest dimension; the transversedirection of the treatment transducer, in contrast, is the directionperpendicular to the acoustic axis following which the dimension of thetreatment transducer is the smallest.

FIG. 1 shows the probe body 2, as well as a part of the patient 4 duringtreatment. The probe body is mounted in rotation on a probe support (notrepresented), by a connection 6; the axis 8 is the axis of rotation ofthe probe body on the probe support. In its frontal part, which isdirected towards the zone of the patient to be treated, the probe bodyhas the treatment transducer 10. The example in the figure is a bevelledtransducer, as shown in FIG. 3. The treatment transducer has in theexample a natural focusing, due to its shape; it could also be formedfrom a plurality of transducers which can be excited independently, andhave electronic focusing. The end of the probe body is formed by a smallballoon 12, which is flexible and transparent to ultrasound. Thisballoon is inflated by a coupling fluid which is transparent toultrasound, using fluid conduits 14 and 16. The conduits are fixed onthe probe body in order to allow easy cleaning, or can be easilychanged; these conduits are terminated by connectors for the injection,extraction or circulation of the coupling fluid; these conduitsadvantageously emerge in the vicinity of the balloon. The coupling fluiddescribed in FR 99 03738 can be used, which is cooled down in order toprotect the treatment transducer against overheating and to protect thesurface of the skin against burning; the fact that the conduits emergein the vicinity of the balloon makes it possible to preferentially cooldown the balloon in the vicinity of the skin. The level of the fluid inthe probe body is chosen—in the example in FIGS. 1 to 3—such that theheight of the fluid and therefore the pressure in the balloon areconstant when passing from the imaging mode to the treatment mode. Thisconstraint does not exist in the example in FIGS. 8 and 9.

Moreover, a mask is provided, the function of which is explained withreference to FIG. 2. The figure also shows the imaging transducer 18, aswell as the plate 20 on which this transducer is mounted in translationfollowing the longitudinal axis of the probe. The imaging transducer is,for example, an ultrasound linear rod, which ensures high-precisionimaging. The rear part 22 of the probe body, opposite the frontal part,contains the transducer displacement actuators.

FIG. 1 also shows the behavior of the ultrasound beam, which, in theplane of the longitudinal direction of the treatment transducer, isconical in shape; the apex of the cone 24 is the focus, on which theultrasound is concentrated. In treatment, the apex covers the target.

As shown in the figure, the axis of rotation 8 of the probe body passessubstantially through the focus, the treatment transducer extends in aplane which is substantially perpendicular to the axis of rotation 8;thus the acoustic axis of the transducer is substantially the same asthe axis of rotation of the probe. In practice, it is advantageous forthe acoustic axis to be exactly the same as the axis of rotation of theprobe—allowing for any mechanical clearances. Nevertheless adisplacement can be allowed between the acoustic axis and the axis ofrotation, to the extent that the displacement of the focal point duringthe rotation of the probe body about the axis of rotation remainslimited, and typically remains smaller than the transverse dimension ofthe focal zone. In terms of distance, the distance between the acousticaxis and the probe axis is advantageously less than 1 mm, throughout thezone extending between the focus and the treatment transducer; in termsof angles, an angle can be allowed between the direction of the acousticaxis and the direction of the axis of rotation of up to 15°.

FIG. 2 is a diagrammatic view in longitudinal section of a probe,following the transverse direction of the treatment transducer. Thefigure shows the elements already described with reference to FIG. 1.FIG. 2 also shows that the treatment transducer is mounted in rotationabout a shaft 24; the rotation of the treatment transducer allows it tobe retracted in order to allow the imaging transducer to pass when theprobe is in the imaging position, as represented in FIGS. 5, 6 and 7.FIG. 2 also shows the function of the mask; due to the presence of theplate 20 and the shaft 24, the probe body is not symmetrical withrespect to the plane containing the axis of rotation and thelongitudinal direction of the treatment transducer. The balloonsurrounds the end of the probe body; the mask 26 has the function oflimiting the deformations of the balloon in the vicinity of the shaft24. Thus, the balloon rests on a rigid contour, defined by the edges ofthe probe body and by the mask; this contour is symmetrical orsubstantially symmetrical with respect to the axis of rotation or withrespect to the acoustic axis 8 of the probe. The inflated balloon thenhas a shape which is symmetrical with respect to the acoustic axis; inparticular, as the figures show, the foremost point of the balloon issubstantially on the acoustic axis. This favors the positioning of theprobe body with respect to the patient. When the probe body is moved inrotation about the axis 8, this ensures that the point of contact or thezone of contact between the balloon and the patient is alsosubstantially on the axis of rotation.

FIG. 2 shows, like FIG. 1, the behavior of the ultrasound beam, which,in the plane of the transverse direction of the treatment transducer, isalso conical in shape; the cone of FIG. 2 however has an angle at thecenter which is smaller than the angle at the center of the cone ofFIG. 1. The difference in angle is representative of the aspect ratio ofthe treatment transducer, in other words the ratio between itslongitudinal dimension and its transverse dimension. In the example, thetransducer has a longitudinal dimension of the order of 54 mm, and atransverse dimension of the order of 35 mm. The ratio between these twodimensions, the aspect ratio of the treatment transducer—is 1.6. Inpractice, aspect ratio values comprised between 2.5 and 1.2 aresuitable. The lower limit is determined by the desire to have apreferential direction for treatment; the upper limit is a function ofthe limitations on the size of the transducers and the ability of theultrasound to pass through the tissues. The focal length of thetransducer depends on the use envisaged and the depth of the organ to betreated. In the case of the thyroid, a focal length between 30 and 45 mmis suitable.

FIG. 2 also shows that the axis of rotation 8 of the probe body passessubstantially through the focus of the treatment transducer. Asexplained above, with respect to the acoustic axis, it is advantageousfor the axis of rotation to be exactly contained within the imagingplane; variations are possible, within the same ranges as those whichare indicated above for the acoustic axis.

FIG. 3 is a diagrammatic front view of the probe body of FIGS. 1 and 2.It shows the treatment transducer, the mask, as well as the axis of theshaft 24. FIG. 3 clearly shows that the contour on which the balloonrests is substantially symmetrical with respect to the axis of rotation.The figure also shows that the treatment transducer is a bevelledtransducer.

FIG. 4 is a diagrammatic view of the probe of FIGS. 1 and 2, being usedfor treatment of the thyroid; the figure represents a cross-section in ahorizontal plane; it shows the skin 28 of the patient's neck, thethyroid 30, the two carotid arteries 32 and 34, as well as the trachea36. The thyroid has two lobes which extend on either side of thetrachea, and are practically in contact with the carotid arteries. Thefigure also shows the position of the ultrasound cone for the treatmentof the right lobe of the carotid; it represents the ultrasound cone 38or 40 for two positions of the probe; the focal zones 42 or 44 are alsorepresented for these two positions of the probe. The figure shows thatthe gland is not very deep and therefore easily accessible to theultrasound. However, in the transverse planes (with reference to thepatient) the acoustic window between the trachea and the external partof the neck is relatively narrow. The elongated shape of the transducer,and the use of the transducer with the longitudinal direction parallelto the neck of the patient makes it possible to have, in the transversedirection, a cone more closed than in the longitudinal direction. Thismakes it possible to keep effective treatment—a given treatmenttransducer surface—whilst preserving the organs adjacent to the gland tobe treated.

The figure does not show the recurrent laryngeal nerves which controlthe vocal chords and pass behind the two lobes of the thyroid gland.These nerves are protected during treatment, to the extent that they aresituated behind the zone aimed at. The esophagus, which is situatedbehind the trachea, is also not shown.

In order to reinforce the safety of the treatment, it is also possibleto use the probe described with a tracheal probe, which is installed inthe patient's trachea during treatments. For example the probe can be anNIM Response® nerve integrity monitor, marketed by the company Xomed. Itcomprises electrodes placed in proximity to the recurrent laryngealnerves, which thus make it possible to detect any alterations to thesenerves due to the ultrasound energy emitted during the treatment.

It is also possible to use a tracheal probe comprising a balloon,positioned facing the thyroid and through which cold water circulates,which makes it possible to cool the trachea down and thus to protect itfrom any thermal damage. A probe combining electrodes and a coldcirculation can also be used.

FIGS. 5, 6 and 7 are diagrammatic views corresponding to FIGS. 1, 2 and3, when the probe is in the imaging position. In this position, thetreatment transducer has tilted about the shaft 24 in order to becomeflattened against the probe body; on the other hand, the plate 20 movesthe imaging transducer 18 forward, so that the latter occupies the placevacated by the treatment transducer. In this imaging position, theimaging plane—or scanning plane of the imaging transducer—contains theaxis of rotation 8 of the probe body. Preferably, the emission surfaceof the imaging transducer is also perpendicular to the axis of rotation8 of the probe body. This plane is parallel to the plane of FIG. 5 andis referenced 46 in FIG. 7. The presence of the plate makes it possibleto move the imaging transducer towards or away from the tissue, in orderto optimize the quality of the image. In fact, in certain cases,parasitic echoes are superimposed on the focal zone and the translationof the probe makes it possible to displace them. Moreover, certainultrasonographs have a fixed focal length, and the displacement of theimaging transducer makes it possible to situate the target within therange in which the image is finest.

In the probe's imaging position, the imaging plane contains the acousticaxis, and therefore also contains the axis of rotation of the probebody. It is therefore possible, during the rotation of the probe body,to obtain in a continuous fashion, the image of the zone of the organ tobe treated which is covered by the target. It is also possible to markon the ultrasonographic image the position of the focus or even theposition or extent of the lesions which will be made by the treatmenttransducer.

In order to return to the treatment position represented in FIGS. 1 to3, the imaging transducer is withdrawn towards the rear of the probebody, and the treatment transducer is pulled down into place, in such away that its acoustic axis is again the same as the axis of rotation ofthe probe body. Retraction of the imaging transducer during treatmentmakes it possible to have a maximum emission surface for the treatmenttransducer.

FIGS. 8 and 9 are partial diagrammatic views of another example of aprobe, in longitudinal section following the longitudinal direction ofthe treatment transducer and in front view. The example of FIGS. 8 and 9differs from the example of the previous figures in that the imagingtransducer is integrated into the treatment transducer; in the example,the imaging transducer is placed in an aperture made in the treatmenttransducer. This makes any displacement of the imaging transducer or thetreatment transducer unnecessary; consequently, the treatment transducerand imaging transducer can be in a fixed position inside the probe body.The latter can be symmetrical in shape with respect to the axis ofrotation, and therefore, the mask is not necessary.

FIG. 8 therefore shows the wall 48 of the probe body, the balloon 50arranged at its front end, the transducer 52 with the part 54 servingfor the imaging and the part 56 serving for the treatment. Aspreviously, the cone 58 formed by the ultrasound, the axis of rotation60 and the patient's skin 62 have been included in the figures. As inthe previous example, the treatment transducer is elongated in shape andits acoustic axis is substantially the same as the axis of rotation ofthe probe body.

FIGS. 10 and 11 are views of the position of the probe body with respectto a patient, being used in treatment of the thyroid; they showdiagrammatically the patient 64, as well as a probe 66 or 68, inposition in the vicinity of the left lobe or the right lobe of thethyroid. For the patient, the longitudinal direction is the directiongoing from the patient's head to feet, and the transverse direction isthe direction going from one lobe of the thyroid to the other lobe.

FIG. 10 shows an imaging position of the probe body. In this position,the patient is recumbent and the probe is brought into contact with theskin of the patient's neck, facing the lobe concerned of the thyroid.The axis of rotation of the probe is then in a vertical plane,perpendicular to the transverse direction of the patient. As symbolizedby the arrow 70 in FIG. 10, it is possible to move the probe body inrotation, about the axis of rotation, this makes it possible to vary theimaging plane of the imaging transducer.

FIG. 11 shows a treatment position of the probe body. In this position,the longitudinal axis of the treatment transducer is parallel to thepatient's longitudinal axis. The elongated shape of the treatmenttransducer allows more precise treatment, without the risk of damagingthe organs adjacent to the thyroid lobes.

FIG. 12 is a diagrammatic view of an example of a probe, showing thesupport of the probe body; this comprises a bracket 72, on which atranslation plate 74 is mounted, by means of a ball-and-socket joint 76.A second translation plate 78 is mounted on the first plate, with adisplacement direction perpendicular to that of the first plate. Theprobe body is mounted in rotation on the second plate 78, with a axis ofrotation perpendicular to the displacement directions of the two plates.The directions x, y and z of the axis of rotation, the displacementdirection of the second plate and the displacement direction of thefirst plate thus form an orthonormal marker.

FIG. 13 is a view analogous to that in FIG. 12, for another example of aprobe support; the probe support in FIG. 13 differs from that in FIG. 12in that the first plate 74 is mounted on the bracket by means of an arch80, along which the first plate can move. The arch 80 is itself mountedin rotation on the bracket according to a vertical axis, which makes itpossible to incline the probe in all directions. It is advantageous forthe radius of the arch to be such that the displacement of the firstplate 74 along the arch takes place about the focus. In other words, theradius of the arch is substantially equal to the distance between thearch and the focus.

In either case, the two plates allow displacement of the probe,perpendicularly to the acoustic axis. In fact, each acoustic pulsecauses necrosis of the tissue in a small volume. In order to treat acomplete target, the head is thus displaced between the firings, bymeans of the plates.

It is also advantageous to orient the front part of the probesubstantially perpendicular to the skin. This makes it possible to keepa constant depth from one displacement of the head to another. Theorientation is possible by means of the ball-and-socket joint in FIG. 12or the arch in FIG. 13. Both ensure a constant depth.

The probe described has the following advantages. First it ensuresprecise marking. In fact, the treatment transducer is combined with animaging transducer, procuring a very fine image and capable ofvisualizing the whole target. To the extent that the relative positionsof the treatment transducer and of the imaging transducer can bedetermined precisely—in both examples—the images obtained by means ofthe imaging transducer are in a known and precise spatial relationshipwith the focal zone of the treatment transducer; the effect of theultrasound is produced well in the zone visualized by the imagingtransducer. The rotation of the probe body about an axis which is thesame as the acoustic axis of the treatment transducer and which iscontained in the imaging plane ensures high precision, even duringdisplacements of the probe.

The probe also ensures safe treatment, in particular in the case oftreatments of the thyroid. The recurrent laryngeal nerves are protectedby the two lobes of the thyroid gland. The depth positioning of thefocal point, by appropriate inflation of the balloon, ensures highprecision depth treatment. The trachea is protected by the positioningof the probe body. The esophagus is situated behind the trachea andprotected by the latter. The high volume of blood flow in the carotidprotects it from the thermal effects of the ultrasound. As explainedabove, the elongated shape of the treatment transducer makes it possibleto preserve the tissues, by using an ultrasound beam in the form of aflattened cone.

The probe also ensures effective treatment. In order to obtain atreatment effect, for example by coagulation of the tissue in the focalzone, the ultrasound waves must be sufficiently concentrated. For thispurpose, the diameter of the transducer is generally allowed to be equalto its focal length. Moreover, the power is a function of the emissivesurface. The elongated shape of the transducer makes it possible tosatisfy the requirement relating to the diameter of the transducer,without reducing the emissive surface.

The probe is also simple to use. In fact, it can easily be adapted toall patients—the contact area of the probe—the projection onto thepatient following the acoustic axis, or the probe's contact zone withthe patient is minimal, and corresponds substantially to the size of thetherapy transducer.

An example of the probe's functioning sequence is now described, withreference to FIG. 14. Reference is made to a screen, which can indicateto the operator the instructions to be followed and allow him tovisualize the images obtained by the imaging transducer, as well as themeans of entering the target limits; these entry means can typicallycomprise a pointing device of any kind. The whole treatment is thencomputer-controlled; the use of a computer or similar equipment forcontrolling an ultrasound treatment appliance is known per se and is notexplained in detail.

At step 82, the operator starts by indicating which side of the patientis treated—right or left. The longitudinal orientation of the probedepends on the side to be treated, as shown in FIG. 11. The probe isthen switched to marking or imaging mode. This can consist of passingfrom the position in FIG. 1 to that in FIG. 5. Alternatively, in thecase of the probe in FIG. 8, it is sufficient to switch the pulsegenerator of the imaging and treatment transducers.

At step 84, the probe is applied to the patient and oriented in thelongitudinal axis of the patient. At this step, the transducer, itsacoustic beam and the future lesion can be symbolized on the screen. Thepractitioner marks on the image the extreme positions “head” and “feet”,which correspond to the cephalo-caudal extension of the target. Thismarking defines a series of “sections” or successive treatment planes,which are oriented transversally with respect to the patient. Thepractitioner also marks the position of the skin, for subsequentcalculation of the power to be delivered during the firings. This stepmakes it possible to determine the successive positions of the probe,following the longitudinal direction of the patient. The distancebetween the “sections” is a function of the size of the zone surroundingthe focus in which the tissues are treated. A distance between 10 and 30mm is suitable.

At step 86, the probe is then displaced towards the first section, whichis the position marked “head”. The probe can then be oriented in thetransverse axis of the patient. To this end, the transducer, itsacoustic beam as it will be during treatment, i.e. when the probe isoriented longitudinally, and the future lesion are symbolized on thescreen. The operator can mark the lesions to be treated in the firstsection.

The operator then displaces the probe towards the second section, in thecaudal direction. He follows the same procedure as for the firstsection, marking the skin and lesions to be treated in this secondsection. The probe is then displaced towards the following sections,carrying out the marking each time.

At the end of these steps 82 to 86, the contours of the target aredetermined, and in each section the limits chosen by the operator forthe ultrasound treatment are known. A different procedure can of coursebe followed, for example reversing the scanning directions and using“vertical sections”. However the marking of the contours of the targeton the horizontal sections makes it easier to avoid the structures to bepreserved, such as the trachea, or the nerves, because these can easilybe seen on the transverse sections through the neck. During steps 84 and86, it is possible to turn the probe, in order to vary the direction ofthe imaging plane, as explained in detail above.

At step 88, the probe is then switched to firing mode; this can consistof passing from the position in FIG. 5 to that in FIG. 1. Alternatively,in the case of the probe in FIG. 8, it is sufficient to re-switch thetransducers' pulse generator; the probe is positioned in rotation insuch a manner that the longitudinal axis of the treatment transducer isthe same as the patient's longitudinal axis. The treatment is thencarried out, by scanning the target following the position parametersdefined in steps 84 and 86. Indications relating to the treatmentparameters are given below. Preferably, and because there is always arisk of the patient moving, the first firings take place in proximity tothe structures to be preserved. In the case of treatment of the thyroid,it is preferable to treat the internal plane first, based on thesupposition that the position of the patient at the start of a treatmentsequence is correct, and that if it evolves, it only does so afterwards.In the vertical direction, it is preferable to treat the caudal sectionsfirst.

By way of example, possible treatment parameters are now given, in thecase of the thyroid. FIG. 15 shows a view of the treatment transducerwith the notations used. The figure includes a diagrammaticrepresentation of the treatment transducer 90, the skin 92, and thetarget 94. The figure shows the focal length—the distance between thetreatment transducer and the focus measured on the acoustic axis 96. Italso shows the distance between the treatment transducer and the skin,also measured along the acoustic axis. The figure shows, in continuouslines, one position of the treatment transducer, and in broken lines,another position of the treatment transducer.

The following notations are used:

f excitation frequency of the transducer

P_(ref E) reference power of the transducer in W: this is the electricalpower to be supplied for the transducer to generate the intensityrequired at the focus in order to obtain coagulation necrosis of thetissues in the focal zone;

η electro-acoustic yield of the transducer: ratio between the acousticpower supplied by the transducer and the electric power used;

P_(ref A) reference power of the transducer in W: this is the electricalpower which must be supplied by the transducer in order to obtaincoagulation necrosis of the tissues in the focal zone; it is defined byP_(ref A)=P_(ref E)*η

D_(foc) focal length of the transducer. Short focal lengths will bepreferable for thin patients;

Φ_(tot) diameter of the transducer, or dimension of the transduceraccording to its longitudinal direction;

Φ_(trunc) truncated diameter of the transducer or dimension of thetransducer according to its transverse direction;

The latter two parameters can be expressed as a function of “theaperture” which is the ratio between the large diameter and the focallength. N=Φ_(tot)/D_(foc) and the truncation parameterR=Φ_(trunc)/Φ_(tot) which is the inverse of the aspect ratio discussedabove.

It is also noted that:

D_(L) spacing between the points in the longitudinal direction;

D_(T) spacing between the points in the transverse direction;

T_(on) duration of each pulse;

T_(off) interval between each pulse.

The power can be calculated by compensating for the absorption of thetissues by an increase in the power according to the formula:P=P _(ref)*exp(2*α*1*D _(ep)/10)

where:

α, absorption coefficient of the tissues in Np/cm/MHz. For HIFUtreatments, a value (0.06 to 0.08) will be used which is higher thanthose given by various bibliographical sources, which can be used inultrasonography (typically 0.04 to 0.05).

D_(ep) thickness of the tissues crossed in mm

D_(ep) is a function of the distance to the skin and the focal length,

D_(ep)=D_(foc)−S with:

SDistance from the transducer to the skin.

It has been shown experimentally that the following parameters areparticularly suitable for the treatment of thyroid nodules in humans.The minimum and maximum permitted values are designated minn and maxx,the recommended value range limits min and max, and Typ is a typicalvalue considered by way of example.

minn Min Typ max maxx Pref A W 5 9 11 13 18 Reference power of thetransducer α Np/cm/ 0.05 0.06 0.07 0.08 0.1 Absorption co- MHz efficientof the tissues F MHz 2 2.5 3 3.5 4.5 Excitation fre- quency of thetransducer Dfoc mm 25 30 40 45 50 Focal length of the transducer S mm 1012 15 25 40 Distance from the transducer to the skin N 1.00 1.04 1.251.36 1.43 Transducer aperture R 51%  61%  70%  76% 100% Transducertruncation DL mm 1.6% 1.7% 1.8% Spacing of points in the longitudinaldirection DT mm 1.6% 1.7% 1.8% Spacing of points in the transversedirection Ton s 2 2.5 3 3.5 6 Duration of each pulse Toff s 3 5 10 15 20Interval between each pulse

These values allow treatment in one session of a unit/total duration ofapproximately 15 minutes. It is found, over a period of several weeksafter the treatment, that the nodules disappear, the tissue treatedbeing replaced by a fibrosis.

Of course, the present invention is not limited to the examples andembodiments described and represented, but it is capable of a number ofvariants accessible to a person skilled in the art. It would thus bepossible to use other elongated shapes of treatment transducers. Thekinematics of the imaging transducer and the treatment transducer can bedifferent from that mentioned in FIGS. 1 to 7. Thus it would be possibleto provide a third displacement for the probe, parallel to the acousticaxis, if the practitioner wishes to move the probe away from or towardsthe tissue. The ball-and-socket joint in FIG. 12 can be replaced by twoperpendicular axes.

It is also clear that the probe is not limited to the preferred use oftreatment of the thyroid; it can also be used for the treatment of otherorgans, such as for example tumors in the neck region, breast tumors,bone tumors or any other organ or tissue anomaly accessible toultrasound by extracorporeal route. The firing parameters provided inthe table can be modified, depending on the organ to be treated, thetherapeutic effect sought, transducer characteristics etc.

Specific embodiments of a treatment probe for focused ultrasoundaccording to the present invention have been described for the purposeof illustrating the manner in which the invention may be made and used.It should be understood that implementation of other variations andmodifications of the invention and its various aspects will be apparentto those skilled in the art, and that the invention is not limited bythe specific embodiments described. It is therefore contemplated tocover by the present invention any and all modifications, variations, orequivalents that fall within the true spirit and scope of the basicunderlying principles disclosed and claimed herein.

1. A treatment probe for coagulating a target by applying focusedultrasound at the target, comprising: a probe body mounted for rotationabout a rotation axis, the probe body carrying a treatment transducerand an imaging transducer; wherein the treatment transducer coagulatesthe target by emitting focused ultrasound along an acoustic axis towardsa focus, in which the focused ultrasound forms a cone having an apex,said apex being the focus and the cone having an angle at the apex whichis less open in a first direction of the treatment transducer than in asecond direction of the treatment transducer; and wherein the imagingtransducer that is capable of obtaining an image of the target; whereinthe treatment probe has a treatment mode in which the acoustic axis ofthe treatment transducer is substantially the same as the rotation axisto allow the probe body to turn about the rotation axis without causingthe focus to move relative to the target; wherein the treatment probehas an imaging mode in which the imaging transducer has an imaging planethat contains the acoustic axis of the treatment transducer as locatedin the treatment mode to allow the probe body to turn about the rotationaxis while the target remains in the imaging plane; and wherein thetreatment probe is arranged to allow moving the probe body exclusivelyby rotation around the rotation axis.
 2. The probe according to claim 1,wherein the treatment transducer is moveably mounted in the probe body.3. The probe according to claim 2, wherein the treatment transducer isrotatably mounted in the probe body.
 4. The probe according to claim 3,wherein the treatment transducer rotates, about an axis perpendicular tothe rotation axis of the probe body.
 5. The probe according to claim 1,wherein the imaging transducer is moveably mounted in the probe body. 6.The probe according to claim 5, wherein the imaging transducer isconfigured for translating in the probe body.
 7. The probe according toclaim 6, wherein the imaging transducer is configured for translatingalong a direction parallel to the rotation axis of the probe body. 8.The probe according to claim 1, wherein the imaging transducer is anarray carrying out a linear scan.
 9. The probe according to claim 8,wherein the imaging transducer comprises a linear scan axis, the linearscan axis being parallel to a longitudinal direction of the treatmenttransducer.
 10. The probe according to claim 1, wherein the imagingtransducer is integrated in the treatment transducer.
 11. The probeaccording to claim 1, including a support on which the probe is mountedfor rotation, the support translationally displacing the probe in aplane perpendicular to the rotation axis.
 12. The probe according toclaim 11, wherein the support translationally displaces the probefollowing the direction of the rotation axis.
 13. The probe according toclaim 11, wherein the support has a ball-and-socket joint fororientation of the probe.
 14. The probe according to claim 11, whereinthe support has an arch along which the probe moves.
 15. The probeaccording to claim 14, wherein the radius of the arch is substantiallyequal to the distance between the arch and the focus of the treatmenttransducer.
 16. The probe according to claim 1, wherein the firstdirection comprises a transverse direction of the treatment transducerand the second direction comprises a longitudinal direction of thetreatment transducer.
 17. The probe according to claim 1, wherein; anend of the probe body is formed by a balloon that is flexible andtransparent to ultrasound, the balloon being adapted to be inflated byan ultrasound-transparent coupling fluid, and the balloon rests on arigid contour symmetrical with respect to the acoustic axis of thetreatment transducer, the inflated balloon having a foremost point whichis substantially on the acoustic axis.
 18. The probe according to claim17, wherein the inflated balloon has a shape that is symmetrical withrespect to the acoustic axis.
 19. The probe according to claim 18,wherein: the probe body is not symmetrical with respect to a planecontaining the rotation axis of the probe body and a longitudinaldirection of the treatment transducer; and the rigid contour on whichthe balloon rests is defined by the edges of the probe body and by acover.
 20. An ultrasound treatment apparatus, comprising: a treatmentprobe for coagulating a target by applying focused ultrasound at atarget, comprising: a probe body mounted for rotation about a rotationaxis, the probe body carrying a treatment transducer and an imagingtransducer; the treatment transducer being configured for emittingfocused ultrasound along an acoustic axis towards a focus, in which thefocused ultrasound forms a cone, having an apex, said apex being thefocus and the cone having an angle at the apex which is less open in afirst direction of the treatment transducer than in a second directionof the treatment transducer; and the imaging transducer being configuredfor obtaining an image of the target; wherein the treatment probe has atreatment mode in which the acoustic axis of the treatment transducer issubstantially the same as the rotation axis to allow the probe body toturn about the rotation axis without causing the focus to move relativeto the target; wherein the treatment probe has an imaging mode in whichthe imaging transducer has an imaging plane that contains the acousticaxis of the treatment transducer as located in the treatment mode toallow the probe body to turn about the rotation axis while the targetremains in the imaging plane; and wherein the treatment probe isarranged to allow moving the probe body exclusively by rotation aboutthe rotation axis; said ultrasound treatment apparatus furthercomprising: a screen allowing images obtained by the imaging transducerof the probe to be viewed; means for symbolizing, on the screen, thetreatment transducer of the probe, and the target to be treated; meansfor entering limits of the target; and a computer configured forcontrolling treatment.
 21. The ultrasound treatment apparatus accordingto claim 20, in which said first circuit is adapted to symbolize on thescreen said acoustic beam as located during treatment, at a point intime when the treatment probe has an orientation transverse to that atthe time of treatment.
 22. A treatment probe for coagulating a target byapplying focused ultrasound at a target, comprising: a probe bodymounted for rotation about a rotation axis, the probe body carrying atreatment transducer and an imaging transducer; the treatment transducerbeing elongated in shape and configured to coagulate the target byemitting focused ultrasound along an acoustic axis towards a focus; andthe imaging transducer configured for obtaining an image of the target;wherein the treatment probe has a treatment mode in which the acousticaxis of the treatment transducer is substantially the same as therotation axis to allow the probe body to turn about the rotation axiswithout causing the focus to move relative to the target; wherein thetreatment probe has an imaging mode in which the imaging transducer hasan imaging plane that contains the acoustic axis of the treatmenttransducer as located in the treatment mode to allow the probe body toturn about the rotation axis while the target remains in the imagingplane; and wherein the treatment probe is arranged to allow moving theprobe body exclusively about the rotation axis.
 23. The probe accordingto claim 22, wherein the treatment transducer has an emitting surfacewith a longitudinal dimension and a transverse dimension and an aspectratio between the longitudinal dimension and the transverse dimensionwhich is greater than 1.2.
 24. The probe according to claim 22, whereinthe treatment transducer has an emitting surface with a longitudinaldimension and a transverse dimension and an aspect ratio between thelongitudinal dimension and the transverse dimension smaller than 2.5.25. The probe according to claim 22, wherein the treatment transducerhas an emitting surface with a longitudinal dimension and a transversedimension and an aspect ratio between the longitudinal dimension and thetransverse dimension greater than 1.2 and smaller than 2.5.